The invention relates to a rotary pulping machine for the extraction of fruit and vegetable juices and purees.
The prior art for the extraction of juices and puree envisages the use of single-or multi-stage extractors of the rotary type.
Such extractors generally comprise a rotor with radial blades which impresses centrifugal forces on the product sufficient to cause the product to pass through a sieve of the cylindrical or conical type, made in perforated sheet steel and surrounding the rotor, and thereafter to be collected externally, while the bits or waste stay inside the sieve and can be removed separately through a special waste discharge outlet.
Where a rather high degree of product refinement is required, eliminating solid impurities larger than a prefixed qualititive standard permits, a first known regulating modality is that of placing two or three extracting machines in series in order to create several extracting stages, with a consequent increase in costs and constructional complexity since in effect the single extractor is doubled or tripled in number, together with its relative motorization.
A second realisation, more often adopted since more economical, envisages the use of one single-stage extractor which performance is increased by increasing the rotation velocity of the rotor, increasing in turn the rotor rotation speed and proportionally the centrifugal forces bearing on the product, or reducing the distance between the rotor blades and the internal surface of the sieve.
With higher rotation velocities, however, the risk of sieve breakage is also increased, since the latter is subject to constant stress, the final result being that the entire machine is less reliable. The sieves used usually have a breadth which is equal to the diameter of the holes, so it is obvious that if a single sieve with very small perforations is used, to allow through only the most refined product, the breadth of that sieve will have to be rather small and thus subject to possible breakage.
This problem is resolved in various-stage extractors by the use of several sieves having breadth and perforation diameters which decrease in cascade, in such a way that the final sieves with fine perforations undergo stress which is inferior to that of the above since the said sieves are in contact with a product that has already been partially refined.
In single-stage machines, the necessary increase in the rotation speed of the rotor and the consequently greater centrifugal forces impressed lead to the fragmentation of the bits (seed fragments, peel), with their subsequent possible passage through the sieve perforations and an ensuing drop in the quality of the final product.